Method and system for preventing execution of a dirty virtual machine on an undesirable host server in a virtualization cluster environment

ABSTRACT

A method for preventing a dirty virtual machine from executing on an undesirable host server includes receiving, by a caching module provided for a first host server that hosts a virtual machine, a write data that is of the virtual machine and that is to be cached for the first host server. The virtual machine uses a virtual hard disk supporting hyper-V Virtual hard disk (VHDX) and virtual hard disk (VHD) file formats or any virtual file format with uniquely identifiable metadata. In response to the receipt of write data, the caching module provided for the first host server changes metadata of virtual hard disk files to a custom format before the virtual machine migrates from the first host server to a second host server, and the virtual machine becomes dirty as a result. When the dirty virtual machine sends a migration request to the second host server, a caching module provided for the second host server checks whether the custom format of the virtual hard disk files is identifiable. If not, then the second host server rejects the migration request initiated by the virtual machine.

PRIORITY

This U.S. non-provisional patent application claims priority under 35U.S.C. § 119 to Indian Patent Application No. 201741030436, filed onAug. 28, 2017 in the Indian Intellectual Property Office, the entirecontents of which are incorporated herein by reference.

BACKGROUND 1. Technical Field

The present disclosure generally relates to cache memories. Moreparticularly, the present disclosure relates to a method and a systemfor preventing execution of a dirty virtual machine on an undesirablehost server in a virtualization cluster environment.

2. Description of the Related Art

Computer memories can be characterized in different forms, including asslowest memories and fastest memories. The slowest memories may presentfarthest from a central processing unit (CPU) in a form of virtualmemories, such as a hard disk drive or remote storage. The fastestmemories may present nearest to CPU in a form of main memory, cachememories, and multiple (a plurality of) registers. Among these, the mainmemory is the slowest. The cache memories are used to store two types ofdata, namely a read-only data and read/write data. When read-only datais cached, data that is stored in and read from the main memory can bestored in a cache memory so that the next time the data needs to beread, it can be read from the (faster) cache memory rather than the(slower) main memory. An example of read-only data that is cached forthe main memory is instructions for a program. Mostly, the read-onlydata is not prone to data loss since any data that gets corrupted in thecache memory can always be read from the main memory.

When read/write data is cached, data to be written to the main memorycan instead or also be written to the cache memory. The way that a cachememory handles writes is called the “write policy” of the cache. Thereare different write policies, two of which are described below.

One such write policy is a write-back cache policy. When data is to bewritten to main memory at a first memory location that is insteadcurrently cached, the new data is only written to a cache line of thecache memory, and not to the main memory. Correspondingly, if a secondmemory location needs to use the cache line where data is currentlystored, the currently stored data needs to be saved—i.e., writtenback—to the first memory location of the main memory so that the cacheline can be used by the second memory location of the main memory.Another write policy is a write-through cache policy. In this method,whenever data is to be written by a processor to main memory at a firstlocation that is also currently cached, both the cache memory and theunderlying memory location are updated. The write-back cache policyprovides better performance than the write-through cache policy at therisk of memory integrity, as the write-back cache policy is prone todata loss due to cache errors.

One write-back caching solution, namely a single state drive (SSD)caching solution, is used in an example scenario shown in FIG. 1. FIG. 1illustrates an example high level view of a virtualization clusterecosystem/environment. The virtualization cluster environment providesinfrastructure for running virtual machines (VMs) and other featuressuch as high availability, shared storage, migrations on failure and soon. Virtual machines are an emulation of a computer system, and anexample of a virtual machine is such an emulation that is designed toexecute computer programs independent of platforms, i.e., without beingnecessarily tied only to a single platform. Some of the virtualizationcluster ecosystems are HyperV, kernel-based virtual machine (KVM) Esxietc. As shown in FIG. 1, the virtualization cluster eco-system includesN host servers, virtual machine VM and virtual machine VM′, one or moresingle state drivers (SSDs) and a remote storage. As illustrated, thevirtual machine VM may be hosted on a host server, e.g., HyperV Host 1102 a, and may migrate to HyperV Host 2 102 b. All the N host serversare HyperV enabled and support Hyper-V virtual hard disk (VHDX) and VHDfile formats in the one or more virtual machines hosted one (connectedto) the N host servers. The N host server can have any virtual platformsupport which does metadata based detection for any file format.

Sometimes, the virtual machine VM migrates from a first host server,e.g., HyperV Host 1 102 a, to a second host server, e.g., HyperV Host 2102 b, due to resource grant or connectivity failure. In the failure ofconnectivity, the first host server would not come to know about virtualmachine migration. The write-back caching solution in the SSD flushesdirty data before the virtual machine VM is shown as “started” with thesecond host server. There are also cases where the virtual machine VM inthe cluster environment can migrate to and run on a host server where acaching solution is not present or not enabled. If a dirty virtualmachine VM starts on a host server that lacks a caching solution and ifdirty data is not flushed, a user would see a corrupt virtual machine.

Several solutions exist in the art for addressing the above issue. Onesuch solution provides a cluster that keep polling new hosts as towhether they have a caching solution, and hosts that lack cachingsolutions are eventually removed by the virtualization clusterecosystem. However, polling might hang a virtualization clusterecosystem or there could be a polling time window where a dirty virtualmachine VM chooses the host without a caching solution before pollingdetects that the host lacks a caching solution. Another solutionprovides virtualization platforms with inbuilt support to create moduledependency by changing their virtualization cluster ecosystem. However,some platforms do not provide such support to virtual machines.

Currently, there exists no solution to prevent dirty virtual machinesfrom executing on an undesirable host server that lacks any platformsupport.

Therefore, there is a need for a method and a system to prevent a dirtyvirtual machine from executing on an undesirable host server in aHyper-Virtual environment.

The above-mentioned shortcomings, disadvantages and problems areaddressed herein and which will be understood by reading and studyingthe following specification.

SUMMARY

According to an aspect of the present disclosure, a method of preventingexecution of a virtual machine having dirty data on an undesirable hostserver in a virtualization cluster environment includes receiving, by acaching module of a first host server, a write data that is of a virtualmachine and that is to be cached for the first host server, wherein thevirtual machine comprises virtual hard disk files of a virtual hard disksupporting at least one virtual hard disk file format of hyper-V Virtualhard disk (VHDX) and virtual hard disk (VHD). The method also includeschanging, by the caching module of the first host server, metadata ofthe virtual hard disk files to a custom format after receiving the writedata, and initiating, by the virtual machine, a migration request toestablish communication with a second host server when the virtualmachine loses connection with the first host server. The method furtherincludes checking, by the second host server, whether the custom formatof the virtual hard disk files is identifiable, and rejecting, by thesecond host server, the migration request initiated by the virtualmachine if the custom format of the virtual hard disk files is notidentifiable.

According to another aspect of the present disclosure, a host serverincludes a processor and a memory having a caching module. The cachingmodule is adapted for receiving a write data that is of a virtualmachine and that is to be cached for a first host server, wherein thevirtual machine comprises virtual hard disk files of a virtual hard disksupporting virtual hard disk file formats including hyper-V Virtual harddisk (VHDX) and virtual hard disk (VHD) file. The caching module is alsoadapted for changing metadata of virtual hard disk files of the virtualhard disk to changed metadata of the virtual hard disk files with acustom format after receiving the write data, and enabling the virtualmachine to migrate to another host server with the changed metadata ofthe virtual hard disk files.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The other objects, features and advantages will occur to those skilledin the art from the following description of the preferred embodimentand the accompanying drawings in which:

FIG. 1 illustrates an example high level view of a virtualizationcluster ecosystem/environment.

FIG. 2 is a flow chart diagram illustrating a method of preventing dirtyvirtual machine execution on an undesirable host server, according toone embodiment.

FIG. 3 is a system diagram illustrating a virtualization clusterenvironment for preventing dirty data execution of a virtual machine onan undesirable host server, according to one embodiment.

FIGS. 4A to 4D are flow diagrams illustrating an example method of ahost server for executing read/write operations of a virtual machine ina virtualization cluster environment, according to one embodiment.

FIG. 5 is a block diagram illustrating one or more components of a hostserver used in a virtualization cluster environment, according to oneembodiment.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure provides a method and a system for preventing anexecution of a dirty virtual machine on an undesirable host server. Inthe following detailed description of the embodiments of the disclosure,reference is made to the accompanying drawings that form a part hereof,and in which are shown by way of illustration specific embodiments inwhich the disclosure may be practiced. These embodiments are describedin sufficient detail to enable those skilled in the art to practice thedisclosure, and it is to be understood that other embodiments may beutilized and that changes may be made without departing from the scopeof the present disclosure. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of thepresent disclosure is defined only by the appended claims.

The specification may refer to “an”, “one” or “some” embodiment(s) inseveral locations. This does not necessarily imply that each suchreference is to the same embodiment(s), or that the feature only appliesto a single embodiment. Single features of different embodiments mayalso be combined to provide other embodiments.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless expressly stated otherwise. Itwill be further understood that the terms “includes”, “comprises”,“including” and/or “comprising” when used in this specification, specifythe presence of stated features, integers, steps, operations, elementsand/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations and arrangements of one or more of theassociated listed items.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure pertains. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

The embodiments herein and the various features and advantages detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. Descriptions of well-knowncomponents and processing techniques are omitted so as to notunnecessarily obscure the embodiments herein. The examples used hereinare intended merely to facilitate an understanding of ways in which theembodiments herein can be practiced and to further enable those of skillin the art to practice the embodiments herein. Accordingly, the examplesshould not be construed as limiting the scope of the embodiments herein.

Throughout the document, the term “undesirable host server” refers to ahost server that lacks a write-back caching solution or platformsupport. Further, throughout the document, the terms “host machine” and“host server” are interchangeably used.

The present disclosure describes a method for preventing execution of avirtual machine having dirty data on an undesirable host server in avirtualization cluster environment. In one embodiment, a host serverincludes or is provided with cache memory such as a solid-state drive(SSD) for caching data associated with the virtual machine. The cachememory such as the SSD adapts a write-back caching solution where dataassociated with the virtual machine are first written into cache memoryand can then be written to a memory location in a main memory of thehost server such as when space in the cache memory is needed by anothermemory location in the main memory. Insofar as the virtual machineexecutes on a host such as a host server, the main memory of the hostsuch as the host server may be considered a main memory of the virtualmachine. That is, the main memory of the host such as the host servermay be used by, assigned to, dedicated fully or partially for use by, orotherwise tied to the virtual machine. Additionally, insofar as thecache memory such as the SSD is used by the virtual machine, the cachememory such as the SSD may be considered a cache memory such as an SSDof the virtual machine. That is, the cache memory such as the SSD may beused by, assigned to, dedicated fully or partially for use by, orotherwise tied to the virtual machine.

In some embodiments, the cache memory such as the SSD may reside outsideof the host server. In some other embodiments, the cache memory such asthe SSD may form an integral component on the host server. The data inthe cache memory such as the SSD which matches the data in acorresponding memory location in a main memory of the host such as thehost server is called clean data and data in the cache memory which doesnot match the data in a corresponding memory location in the main memoryis called dirty data. In other words, the recent memory data that isstored in the cache memory of (used by, assigned to, dedicated fully orpartially for use by) the virtual machine is called dirty data when itdoes not match the data in the corresponding memory location in the mainmemory.

Sometimes, the virtual machine having the dirty data may migrate from afirst host machine to a second host machine either due to resource grantby the first host machine or connection failure with the first hostmachine. In some embodiments, the host machine is at least one of acomputing device and a server.

FIG. 2 is a flow chart diagram illustrating a method of preventing dirtyvirtual machine execution on an undesirable host server, according toone embodiment. Depending on the embodiment, additional steps may beadded, others removed, and the ordering of the steps may be changed. Atstep 202, a write data that is associated with a virtual machine andthat is to be cached is received by a caching module of a first hostserver. The caching module then caches the write data associated withthe virtual machine. In one embodiment, the caching module may presentin a caching device such as solid-state drive (SSD) for caching data ofinput/output (I/O) operations of the virtual machine. In thisembodiment, the caching device may present externally to the hostserver. The I/O operations comprise at least one of a read operation anda write operation. The data for the I/O operations is stored in avirtual hard disk of (used by, assigned to, dedicated fully or partiallyfor use by) the virtual machine. The hard disk of the virtual machinesupports both Hyper-V virtual hard disk (VHDX) and VHD file formats.Thus, the write data received in step 202 is cached as a VHDX file or aVHD file in the caching module of the SSD. At step 204, metadata of VHDXand VHD files are changed by the caching module of the SSD of the firsthost server to a custom format when the write command is received. Themetadata of the VHDX and VHD files are changed to the custom format suchthat it can be recognized by any host server having a caching module. Inone embodiment, the virtual machine can support any type of file formatwhich has metadata based detection techniques. The custom format may beone of a set of custom formats pre-arranged for the virtualizationcluster ecosystem/environment that includes the first host server andother host servers, so that host servers to which a virtual machinemigrates will be accepted. The custom format is different than theoriginal format of the metadata of the VHDX and VHD files, and may beused to replace multiple different original formats.

Now, consider that the connection between the first host server and thevirtual machine is lost. Therefore, the virtual machine tends to migratefrom the first host server to a second host server. Since the write dataassociated with the virtual machine is not flushed into a main memory ofthe current host of (used by, assigned to, dedicated fully or partiallyfor use by) the virtual machine before migration, the virtual machinebecomes dirty. At step 206, a migration request is initiated by thedirty virtual machine to establish communication with a second hostserver. The second host server includes or is provided with a cachingdevice such as a SSD for caching data of I/O operations of the virtualmachine. The caching device further includes a caching module toidentify custom format of the VHDX and VHD files. Therefore, at step208, the caching module checks whether the custom format of the VHDX andVHD files of the virtual machine is identifiable by the second hostserver. If the custom format of the VHDX and VHD files of the virtualmachine is not identifiable, at step 210, the migration requestinitiated by the virtual machine is rejected by the second host server,thereby preventing the virtual machine from executing on the second hostserver.

FIG. 3 is a system diagram illustrating a virtualization clusterenvironment for preventing dirty data execution of a virtual machine onan undesirable host server, according to one embodiment. Thevirtualization cluster environment 300 includes at least three hostservers, i.e., host 302 a, host 302 b, and host 302 c. Thevirtualization cluster environment 300 also includes a caching device(SSD 306) and a caching device (SSD 306′), as well as virtual machine304 and virtual machine 304′, and a remote storage 308 which is shared.The virtual cluster environment 300 provides infrastructure for runningvirtual machines and provides features such as high availability, sharedstorage, migrations on host failure and so on. The high availabilityfeature enables a virtual machine to run on another host machine if theconnection with the current host device fails. Some of thevirtualization cluster environment 300 includes, but is not limited to,HyperV, kernel-based virtual machine (KVM), Esxi etc.

In one embodiment, multiple virtual machines run on/in thevirtualization cluster environment and the movement of the virtualmachines is managed based on cluster management policies. The virtualmachine 304 and virtual machine 304′ may be assigned hard disk resourcesto implement a virtual hard disk (VHD) that provides storage space foreach or either of the virtual machine 304 and virtual machine 304′. Asingle virtual machine among virtual machine 304 and virtual machine304′ may be provided with multiple virtual hard disks (VHDs), each ofwhich in turn may have access to memory resources of (actual) harddisks. The virtual machine 304 and virtual machine 304′ supporthyper-Virtual hard disk (VHDX) and VHD file formats and caching isenabled for all VHDs used by the virtual machine 304 and virtual machine304′. The VHDX and VHD files are of Windows file formats adapted for thevirtual machine 304 and virtual machine 304′. The virtual machine 304 isalso capable of supporting any type of file formats such as raw, qcow,vmdk on VMware etc., that can be identified using metadata baseddetection techniques. Each of these file formats may have their ownuniquely identifiable metadata such as signature, strings and the liketo store data of I/O operations in the VHD of the virtual machine. Oneor more signatures of metadata of virtual hard disk files may include aspecific unique string that is uniquely correlated with one or morevirtual hard disk file. The specific unique string may be a set ofcharacters recognized/recognizable to ta caching device. In oneembodiment, the caching device is attached to the host 302 a and/or thehost 302 c for increasing input/output operations per second (IPOS) forthe virtual machine 304 and virtual machine 304′.

A caching module is present in a caching device (SSD 306) for cachingdata of one or more I/O operations of the virtual machine 304. A cachingmodule is also present in another caching device (SSD 306′) as explainedlater. The caching module uses a write-back caching solution for cachingdata of I/O operations of the virtual machine. The caching module isfurther adapted for changing metadata associated with VHDX and VHD fileswhen a write command having write data is received, the metadata beingat least one of a signature and a string. Thus, when a write command isreceived, the metadata of the VHDX and VHD files is changed to a customformat. The metadata is changed to the custom format to make sure thathost servers that have a caching module are able to identify the customformat of the VHDX and VHD files in the virtualization customenvironment.

In this scenario, consider that the virtual machine 304 migrates fromhost 302 a to host 302 b before the caching module in the caching device(SSD 306) flushes the write data to the VHD/VHDX file of the virtualmachine. The host 302 a may be a hyperV host, the host 302 b may be ahyperV host, and the host 302 c may be a hyperV host. Since, the writedata is not flushed, the virtual machine 304 becomes dirty and thecaching module in the caching device (SSD 306) changes metadata of theVHDX and VHD files to the custom format. As shown in FIG. 3, when thevirtual machine 304 initiates a migration request to host 302 b, thehost 302 b checks in response whether it can identify the custom formatof the VHDX and VHD files. Since, the host 302 b does not have thewrite-back caching, the host 302 b does not understand the virtualmachine 304 and rejects the migration request received from the virtualmachine 304.

Now, the virtual machine 304 makes a next migration attempt in thevirtualization cluster environment 300. The virtual machine 304 searchesfor the next host server and eventually finds host 302 c. The host 302 cchecks whether the custom format of the VHDX and VHD files isidentifiable. Since, the host 302 c has write-back caching, host 302 cunderstands the virtual machine 304 and accepts the migration requestreceived from the virtual machine 304. In one embodiment, the signatureof VHDX and VHD files in custom format is converted back to the originalformat of the metadata of the VHDX and VHD files of the dirty virtualmachine. Then, the dirty data of the virtual machine 304 is synced onthe host 302 c. In one embodiment, the caching module present in thecaching device (SSD 306′) of/for the host 302 c obtains the dirty dataof the virtual machine 304 from a different server which has replicatedthe cached data of the virtual machine 304.

FIGS. 4A to 4D are flow diagrams illustrating an example method of ahost server for executing read/write operations of a virtual machine ina virtualization cluster environment, according to one embodiment. FIG.4A illustrates an example method of a host server for executing a readoperation of a virtual machine, according to one embodiment. In thisembodiment, consider that the host server does not have a cachingsolution/module. The step by step process being carried out inpreventing the dirty virtual machine from executing is explained hereinas follows. At step 402, a host server attempts to read data associatedwith a read operation of a virtual machine. The data of the readoperation is stored in one of VHDX file format and VHD file format in avirtual hard disk (VHD) of the virtual machine. The virtual machinefirst reads the signature of the VHDX and VHD files at step 404. Since,the host server does not have a caching module, a platform of the hostserver checks whether the VHDX/VHD file is dirty. In other words, atstep 406 the platform of the host server checks whether the VHDX/VHDfile has any data that is to be flushed. If the VHDX/VHD file is dirty,at step 408, the host server stops the read operation associated withthe virtual machine. If the VHDX/VHD file is not dirty, at step 410, thehost server performs the read operation associated with the virtualmachine. It is to be noted that the host server is capable of accessingany file format whose signature can be detected using metadata baseddetection.

FIG. 4B illustrates an example method of a host server for executing awrite operation of a virtual machine, according to another embodiment.In this embodiment, consider that the host server has a cachingsolution/module. The step by step process being carried out inpreventing the dirty virtual machine from executing is explained hereinas follows. At step 432, a host server having the caching modulereceives a write operation associated with a virtual machine. The hostserver writes the data of the write operations into a caching devicesuch as a solid-state drive (SSD). This is performed at step 434. Thedata of the write operations is written to the SSD in the form of VHDXand VHD files. Further, at step 436, the caching module in the SSD marksthat the VHDX/VHD file is dirty and changes the signature of theVHDX/VHD file to a custom format.

FIG. 4C is a flow diagram illustrating an example method of a hostserver for executing a read operation of a virtual machine, according toanother embodiment. In this embodiment, consider that the host serverhaving a caching module attempts to read a write operation as executedin FIG. 4B even though the signature of VHDX/VHD file is changed.Therefore, at step 452, the host server having the caching moduleperforms a read operation on the VHDX/VHD file of the virtual machine.At step 454, it is checked whether the caching module of the host serveris reading a signature of the VHDX/VHD file or some other data file. Ifa signature of the VHDX/VHD file is read, then the caching modulesearches the signature offset where the metadata of the VHDX/VHD file ispresent and corrects the signature back to the VHDX/VHD file format.This is performed at step 456. It is to be noted that the host servercan have any virtual platform support which does metadata baseddetection for any file format other than VHDX and VHD file formats.

FIG. 4D is a flow diagram illustrating an example method of a hostserver in preventing a dirty virtual machine from executing when thevirtual machine is shut down by a host server, according to oneembodiment. At step 472, the host server attempts to shut down thevirtual machine. While shutting down the virtual machine, the hostserver at step 474, checks whether the VHDX/-VHD file present in thevirtual machine is dirty. To check this, the caching module verifieswhether the signature of the VHDX/VHD file is in the custom format. Ifyes, at step 476, the caching module of the host server syncs the datato the virtual machine and changes the custom format of the signatureback to VHDX/VHD specified file format. In an embodiment, the cachingmodule obtains dirty virtual machine data from a different server whichhas a replica of the cached data of the virtual machine and syncs theobtained dirty data with the host server to which the virtual machine iscurrently connected.

FIG. 5 is a block diagram illustrating one or more components of a hostserver used in a virtualization cluster environment, according to oneembodiment. As shown in FIG. 5, the host server 500 comprises of aprocessor 502, and a memory 504. The memory 504 further includes acaching module 506 for caching one or more input/output operations of avirtual machine.

The processor 502 is adapted for performing one or more instructionsstored in the memory 504. In one embodiment, the processor 502 mayinclude any one or more of a microprocessor, a controller, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field-programmable gate array (FPGA), or equivalent discreteor integrated logic circuitry. Additionally, the functions attributed tothe processor 502, in this disclosure, may be embodied as software,firmware, hardware or any combination thereof.

The memory 504 may, in some examples, be described as acomputer-readable storage medium. The memory 504 may be a volatilememory, meaning that the memory 504 does not maintain stored contentswhen the computer is turned off. Examples of volatile memories includerandom access memories (RAM), dynamic random-access memories (DRAM),static random-access memories (SRAM), and other forms of volatilememories known in the art. In some examples, the memory 504 may be usedto store program instructions for execution by processor 502. Forexample, the memory 504 includes the caching module stored in the formof program instructions for execution by the processor 502.

The caching module 506 is adapted for caching data of one or moreinput/output operations of the virtual machine. The caching module 506is also adapted for changing metadata of VHDX and VHD files to a customformat when a write data is received. The caching module 506 performschanging of metadata of VHDX and VHD files to a custom format to ensurethat execution of the virtual machine on any undesirable host server inthe virtualization cluster environment 300 is prohibited. Thus, thepresent disclosure ensures safety of the virtual machine till the dirtydata is flushed. The present disclosure also prevents data corruption inwrite-back caching in/on the virtualization cluster environment.

The foregoing description of the present disclosure has been providedfor the purposes of illustration and description. It is not intended tobe exhaustive or to limit the disclosure to the precise forms disclosed.Many modifications and variations will be apparent to the practitionerskilled in the art. The embodiments were chosen and described in orderto best explain the principles of the disclosure and its practicalapplication, thereby enabling others skilled in the art to understandthe disclosure for various embodiments and with various modificationsthat are suited to the particular use contemplated. It is intended thatthe scope of the disclosure be defined by the following claims and theirequivalence. Examples of modifications and variations within the scopeof the present disclosure are provided in the paragraphs that follow.

According to one embodiment, the virtual machine migrates from the firsthost server to the second host server when the first host server isunable to grant resources or is unable to provide connectivity to thevirtual machine.

According to another embodiment, the metadata of the virtual hard diskfiles includes at least one signature.

According to still another embodiment, the at least one signature of themetadata of the virtual hard disk files includes a specified uniquestring.

According to one embodiment, the method further includes converting theat least one signature of the metadata of the virtual hard disk files tothe custom format. The custom format includes a set of charactersrecognized by the caching module

According to another embodiment, the virtual machine after the rejectingof the migration request performs at least one of: an attempt toreconnect with the first host server, and an attempt to connect with ahost server having a caching module identified by a virtualizationcluster environment.

According to still another embodiment, the method further includesconverting the at least one signature of the metadata of the virtualhard disk files in the custom format back to virtual hard disk files ofthe virtual machine having dirty data, and syncing dirty data of thevirtual machine having dirty data on the second host server if thecustom format of the virtual hard disk files is identifiable by thesecond host server.

According to yet another embodiment, the syncing of the virtual machinehaving dirty data includes obtaining dirty data of a virtual machinehaving dirty data from a different server which is a replica server forcached data of the virtual machine having dirty data.

According to another embodiment, the second host server is capable ofoperating on any virtual platform that supports metadata based detectionfor any file format.

According to still another embodiment, the method further includesattempting, by the second host server, to read data associated with aread operation of the virtual machine, wherein the second server doesnot have the caching module. The method also includes reading, by thesecond server, a signature of the virtual hard disk (VHD) of the virtualmachine and checking, by the second host server, whether the at leastone virtual hard disk file format is identifiable, and stopping, by thesecond host server, reading of data associated with the read operationof the virtual machine if the at least one virtual hard disk file formatis not identifiable.

What is claimed is:
 1. A method of preventing execution of a virtualmachine having dirty data on an undesirable host server in avirtualization cluster environment, the method comprising: receiving, bya caching module of a first host server, a write data that is of-a thevirtual machine (VM) and that is to be cached for the first host server,wherein the virtual machine comprises virtual hard disk files of avirtual hard disk supporting at least one virtual hard disk file formatof hyper-V Virtual hard disk (VHDX) and virtual hard disk (VHD);changing, by the caching module of the first host server, metadata ofthe virtual hard disk files of the virtual hard disk to a custom formatafter receiving the write data, wherein the metadata of the virtual harddisk files comprises a specified unique string: initiating, by thevirtual machine, a migration request to establish communication with asecond host server when the virtual machine loses connection with thefirst host server and after the changing of the metadata of the virtualhard disk files to the custom format: attempting, by the second hostserver, reading data associated with a read operation of the virtualmachine: reading, by the second host server, the specified unique stringof the virtual hard disk (VHD) of the virtual machine: checking, by thesecond host server, whether the custom format of the metadata of thevirtual hard disk files is identifiable; and rejecting, by the secondhost server, the migration request initiated by the virtual machine ifthe custom format of the virtual hard disk files is not identifiable. 2.The method of claim 1, wherein the virtual machine migrates from thefirst host server to the second host server when the first host serveris unable to grant resources or is unable to provide connectivity to thevirtual machine.
 3. The method of claim 1, wherein the metadata of thevirtual hard disk files comprises at least one signature comprising thespecified unique string.
 4. The method of claim 3, further comprising:converting the at least one signature of the metadata of the virtualhard disk files to the custom format; wherein the custom format includesa set of characters recognized by the caching module.
 5. The method ofclaim 1, wherein the virtual machine after the rejecting of themigration request performs at least one of: an attempt to reconnect withthe first host server; and an attempt to connect with a host serverhaving the caching module identified by a cluster.
 6. The method ofclaim 3, further comprising: converting the at least one signature ofthe metadata of the virtual hard disk files in the custom format back tothe virtual hard disk files of the virtual machine having the dirtydata; and syncing the dirty data of the virtual machine having the dirtydata on the second host server if the custom format of the virtual harddisk files is identifiable by the second host server.
 7. The method ofclaim 6, wherein the syncing dirty the data of the virtual machinehaving the dirty data comprises: obtaining the dirty data of the virtualmachine having the dirty data from a different server which replicatescached data of the virtual machine having the dirty data.
 8. The methodof claim 1, wherein the second host server is capable of operating onany virtual platform that supports the metadata based detection for anyfile format.
 9. The method of claim 1, further comprising: attempting,by the second host server, reading data associated with a read operationof the virtual machine, wherein the second host server does not have thecaching module; reading, by the second host server, a signature of thevirtual hard disk (VHD) of the virtual machine; checking, by the secondhost server, whether the at least one virtual hard disk file format isidentifiable; and stopping, by the second host server, reading of thedata associated with the read operation of the virtual machine if the atleast one virtual hard disk file format is not identifiable.
 10. A hostserver system comprising a first host server and a second host server,the first host server comprising: a processor: and a memory having acaching module, adapted for wherein the caching module is configured toreceive receiving a write data that is of a virtual machine (VM) andthat is to be cached for-a the first host server, wherein the virtualmachine comprises virtual hard disk files of a virtual hard disksupporting at least one virtual hard disk file format of formatsincluding hyper-V Virtual hard disk (VHDX) and virtual hard disk (VHD);the caching module is configured to change changing metadata of thevirtual hard disk files of the virtual hard disk to changed metadata ofthe virtual hard disk files with a custom format after receiving thewrite data, wherein the metadata of the virtual hard disk filescomprises a specified unique string: -and the virtual machine isconfigured to enabling the virtual machine to migrate to initiate amigration request to establish communication with the second anotherhost server when the virtual machine loses connection with the firsthost server and after the with the changed metadata of the virtual harddisk files is changed: and the second host server is configured to checkwhether the custom format of the metadata of the virtual hard disk filesis identifiable, to attempt to read data associated with a readoperation of the virtual machine, to read the specified unique string ofthe virtual hard disk (VHD) of the virtual machine, and to reject themigration request initiated by the virtual machine if the custom formatof the virtual hard disk files is not identifiable.
 11. The host serversystem as claimed in claim 10, wherein the caching module is furtheradapted for: receiving a migration request of the virtual machine toestablish communication with the second host server when the virtualmachine loses connection with the first host server; checking whetherthe custom format of the virtual hard disk files is identifiable; andrejecting the migration request initiated by the virtual machine if thecustom format of the virtual hard disk files is not identifiable.
 12. Amethod of preventing execution of a virtual machine having dirty data onan undesirable host server in a virtualization cluster environment, themethod comprising: receiving, by a second host server from the virtualmachine comprising virtual hard disk files of a virtual hard disk, amigration request to migrate the virtual machine from a first hostserver after metadata of the virtual hard disk files is changed by acaching module of the first host server upon receiving write data to becached, wherein the metadata of the virtual hard disk files comprises aspecified unique string; checking, by the second host server, whether acustom format of the virtual hard disk files of the virtual machine isidentifiable; attempting, by the second host server, reading dataassociated with a read operation of the virtual machine; reading, by thesecond host server, the specified unique string of the virtual hard disk(VHD) of the virtual machine; rejecting, by the second host server, themigration request from the virtual machine if the custom format of thevirtual hard disk files is not identifiable, wherein the custom formatis a format of the metadata of the virtual hard disk files changed bythe caching module of the first host server upon receiving write data tobe cached, and wherein the virtual machine comprises virtual hard diskfiles of the virtual hard disk that supports at least one hard disk fileformat of hyper-V Virtual hard disk (VHDX) and virtual hard disk (VHD).13. The method of claim 12, wherein the virtual machine migrates fromthe first host server to the second host server when the first hostserver is unable to grant resources or is unable to provide connectivityto the virtual machine.
 14. The method of claim 12, wherein the metadataof the virtual hard disk files comprises at least one signature.
 15. Themethod of claim 12, wherein the virtual machine identifies the secondhost server from a cluster, and attempts to connect with the second hostserver based on the second host server having the caching module. 16.The method of claim 14, further comprising: converting the at least onesignature back to the virtual hard disk file of the virtual machinehaving the dirty data; and syncing the dirty data of the virtual machinehaving the dirty data on the second host server.
 17. The method of claim16, wherein syncing the dirty data of the virtual machine having thedirty data comprises: obtaining the dirty data of the virtual machinehaving the dirty data from a different server which replicates thecached write data of the virtual machine having the dirty data.
 18. Themethod of claim 12, wherein the second host server is capable ofoperating on any virtual platform that supports the metadata baseddetection for any file format.